Hostname: page-component-78c5997874-94fs2 Total loading time: 0 Render date: 2024-11-02T22:49:20.119Z Has data issue: false hasContentIssue false
  • English
  • Français

Microburst modelling and scaling

Published online by Cambridge University Press:  26 April 2006

T. S. Lundgren ,
J. Yao  and
N. N. Mansour
T. S. Lundgren
Affiliation:
Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, MN 55455, USA
J. Yao
Affiliation:
Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, MN 55455, USA
N. N. Mansour
Affiliation:
NASA Ames Research Center, Moffett Field, CA 94035, USA
Get access Rights & Permissions [Opens in a new window]

Abstract

A microburst can be modelled by releasing a volume of fluid that is slightly heavier than the ambient fluid, allowing it to fall onto a horizontal surface. Vorticity develops on the sides of this parcel as it descends and causes it to roll up into a turbulent vortex ring which impinges on the ground. Such a model exhibits many of the features of naturally occurring microbursts which are a hazard to aviation. In this paper this model is achieved experimentally by releasing a volume of salt water into fresh water from a cylindrical dispenser. When care is taken with the release the spreading rate of the surface outflow is measurable and quite repeatable despite the fact that the flow is turbulent. An elementary numerical approximation to this model, based on inviscid vortex dynamics, has also been developed. A scaling law is proposed which allows experiments with different fluid densities to be compared with each other and with the numerical results. More importantly the scaling law allows us to compare the model results with real microbursts.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 239 , June 1992 , pp. 461 - 488
Copyright
© 1992 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Abramowitz, M. & Stegun, I. A., 1972 Handbook of Mathematical Functions. Washington, DC: Government Printing Office.
Dahm, W. J. A., Scheil, M. & Tryggvason, G., 1989 Dynamics of vortex interaction with a density interface. J. Fluid Mech. 205, 1–43.Google Scholar
Dritschel, D. G.: 1988 Contour surgery: a topological reconnection scheme for extended integrations using contour dynamics. J. Comput. Phys. 77, 240–266.Google Scholar
Fujita, T. T.: 1981 Tornadoes and downbursts in the context of generalized planetary scales. J. Atmos. Sci. 38, 1511–1534.Google Scholar
Fujita, T. T.: 1985 The Downburst. The University of Chicago Press.
Fujita, T. T.: 1986 DFW Downburst. The University of Chicago Press.
Higdon, J. J. L. & Pozrikidis, C. 1985 The self-induced motion of vortex sheets. J. Fluid Mech. 150, 203–231.Google Scholar
Ivan, M.: 1986 A ring-vortex downburst model for flight simulation. J. Aircraft 23, 232–236.Google Scholar
Krasny, R.: 1987 Desingularization of Periodic Vortex Sheet Rollup. J. Comput. Phys. 65, 292–313.Google Scholar
Lamb, H.: 1932 Hydrodynamics, Cambridge University Press.
Leonard, A.: 1985 Computing three-dimensional flows with vortex elements. Ann. Rev. Fluid Mech. 17, 523–559.Google Scholar
Lundgren, T. S. & Mansour, N. N., 1991 Vortex ring bubbles. J. Fluid Mech. 224, 177–196.Google Scholar
Maxworthy, T.: 1972 The structure and stability of vortex rings. J. Fluid Mech. 51, 15–32.Google Scholar
Maxworthy, T.: 1974 Turbulent vortex rings. J. Fluid Mech. 64, 227–239.Google Scholar
Meiron, D. I., Baker, G. R. & Orszag, S. A., 1982 Analytical structure of vortex-sheet dynamics. Part 1. Kelvin–Helmholtz instability. J. Fluid Mech. 114, 283–298.Google Scholar
Moore, D. W.: 1979 The spontaneous appearance of a singularity in the shape of an evolving vortex sheet. Proc. R. Soc. Lond. A 365, 105–119.Google Scholar
Orlandi, P.: 1990 Vortex dipole rebound from a wall. Phys. Fluids A 2, 1429–1436.Google Scholar
Pozrikidis, C. & Higdon, J. J. L. 1985 Nonlinear Kelvin–Helmholtz instability in a finite vortex layer. J. Fluid Mech. 157, 225–263.Google Scholar
Proctor, F. H.: 1988 Numerical simulations of an isolated microburst. Part I: Dynamics and structure. J. Atmos. Sci. 45, 3137–3160.Google Scholar
Scorer, R. S.: 1957 Experiments on convection of isolated masses of buoyant fluid. J. Fluid Mech. 2, 583–594.Google Scholar
Simpson, J. E.: 1972 Effects of the lower boundary on the head of a gravity current. J. Fluid Mech. 53, 759–768.Google Scholar
Tryggvason, G.: 1989 Simulations of vortex sheet rollup by vortex methods, J. Comput. Phys. 80, 1–16.Google Scholar
Turner, J. S.: 1957 Buoyant vortex rings. Proc. R. Soc. Lond. A 239, 61–75.Google Scholar
Walker, J. D. A., Smith, C. R., Cerra, A. W. & Doligalski, T. L., 1987 The impact of a vortex ring on a wall. J. Fluid Mech. 181, 99–140.Google Scholar
Wilson, J. W., Roberts, R. D., Kessinger, C. & Mccarthy, J., 1984 Microburst wind structure and evaluation of Doppler radar for airport wind shear detection. J. Climate Appl. Met. 23, 898–915.Google Scholar
Zhu, S. & Etkin, B., 1985 Model of the wind field in a downburst. J. Aircraft 22, 595–601.Google Scholar